1. Field
The presently disclosed subject matter relates to headlight controllers and vehicle headlight systems, and more particularly to vehicle headlight systems including the headlight controller and optical unit, which do not include a movable component with a simple structure, and the vehicle headlight systems having a favorable light distribution pattern, which can be easy to drive at night, can prevent the optical unit from emitting a glare type light to oncoming vehicles and vehicles moving forward on a driving lane even when a drive drives on a curved roadway.
2. Description of the Related Art
When drivers steer a car at night, the drivers usually want to steer the car while they turn on headlights for a high beam to improve a visibility. However, drivers must drive the car while they switch between the headlights for a high beam and headlights for a low beam in response to various traffic conditions so that the headlights do not emit a glare type light to oncoming vehicles, vehicles moving forward on a same driving lane, etc.
Hence, vehicle headlight systems including an adaptive driving beam (ADB) have been developed. A vehicle headlight system including an ADB, for example, may contribute an improvement of visibility in a forward direction of the vehicle that has the ADB for a driver by detecting an oncoming vehicle, a forward vehicle and the like with a camera incorporated into the vehicle that has the ADB and by emitting a high beam for the driver on an area except regions where the oncoming vehicle and the forward vehicle move.
A conventional headlight system including an ADB is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP 2010-232081). FIGS. 7a to 7e are schematic side cross-sectional views depicting a respective one of operations in a conventional headlight of a vehicle headlight system including the ADB, which is disclosed in Patent Document No. 1. The conventional headlight 70 includes: a light source 71; a projector lens 72 located in a light-emitting direction of the light source 71: and a rotatable shutter 73 located between the light source 71 and the projector lens 72, wherein the headlight 70 forms various light distribution patterns using light emitted from the light source 71 via the projector lens 72 by rotating the rotatable shutter 73 in response to various traffic conditions.
FIG. 8a to FIG. 8e are top views depicting exemplary schematic light distribution patterns, which may be formed by the above-described headlight 70 of the headlight system used in countries where drivers keep to the left side of the road. FIG. 8a shows a light distribution pattern Pa for a high beam, when oncoming vehicles and vehicles moving forward on a same driving lane do not exist in a forward direction of a subject vehicle that has the ADB for a driver. In this case, the driver of the subject vehicle may drive on the driving lane while the driver keeps a wide view under the light distribution pattern Pa for a high beam by the headlight 70 shown in FIG. 7a. 
FIG. 8b shows a light distribution pattern Pb for a high beam, when an oncoming vehicle approaches on an oncoming lane in a direction toward the subject vehicle from a long distance. In this case, by rotating the rotatable shutter 73 in the headlight 70 as shown in FIG. 7b, the subject vehicle may drive on the driving lane under the light distribution pattern Pb for a high beam so as not to emit a glare type light to the oncoming vehicle while the driver keeps a wide view under the light distribution pattern Pb for a high beam.
FIG. 8c shows a light distribution pattern Pc for a high beam, when a forward vehicle drives forward on the same driving lane in a forward direction of the subject vehicle from a medium distance. In this case, the subject vehicle may drive on the same driving lane under the light distribution pattern Pc for a high beam so as not to emit a glare type light to the forward vehicle while the driver keeps a wide view under the light distribution pattern Pc for a high beam by rotating the rotatable shutter 73 of the headlight 70 shown in FIG. 7c. 
FIG. 8d shows a light distribution pattern Pd for a high beam, when a forward vehicle drives forward on the same driving lane in a forward direction of the subject vehicle from a medium distance and when an oncoming vehicle approaches on the oncoming lane in a direction toward the subject vehicle from a medium distance. In this case, the subject vehicle may drive on the same driving lane under the light distribution pattern Pd for a high beam so as not to emit a glare type light to the forward vehicle and the oncoming vehicle by using the headlight 7d shown in FIG. 7d. 
Next, when an oncoming vehicle approaches on the oncoming lane in a direction toward the subject vehicle from a medium distance and when a forward vehicle drives forward on the same driving lane in a forward direction of the subject vehicle from a medium distance, as shown in FIG. 8e, the subject vehicle, which has the ADS for a driver, may provide a light distribution pattern Pe for a low beam so as not to emit a glare type light to the oncoming vehicle and the forward vehicle by the headlight 70 for a low beam shown in FIG. 7e, in which a substantially upward light is shaded by the rotatable shutter 73 while a downward light passes through the projector lens 72.
Accordingly, the conventional headlight system including the ADB can provide favorable light distribution patterns using light emitted from the light source 71 via the projector lens 72 by rotating the rotatable shutter 73 in response to various traffic conditions so as not to emit a glare type light to the oncoming vehicle and the forward vehicle, while keeping a wide view for safe driving. However, when the conventional headlight system varies from one of the above-described light distribution patterns to another one, a variation from the one of the light distribution patterns to the other one may carried out at once. Therefore, said rapid variation of a light-emitting intensity may cause an uncomfortable feeling to drivers for the oncoming vehicle, the forward vehicle and the subject vehicle, and also may cause frights to pedestrians.
In order to improve the uncomfortable feeling as described above, a conventional shade control unit is disclosed in Patent Document No. 2 (Japanese Patent Application Laid Open JP 2012-151058), in which a shade performs a role similar to the rotatable shutter of the above-described conventional headlight system including the ADB. According to the conventional shade control unit, when a conventional headlight system using the shade control unit varies from one of light distribution patterns to another one, a rapid variation of a light-emitting intensity may be inhibited by prolonging a time of the rapid variation of the light-emitting intensity.
However, when a subject vehicle having the conventional headlight system using the shade control unit drives, for example, on a curved road and when an oncoming vehicle approaches on an oncoming lane toward the subject vehicle driving on the driving lane, a time while the conventional headlight system changes from a high beam to a light distribution pattern to prevent an emission on an existing region of the oncoming vehicle after detecting the oncoming vehicle may be also subject to a long time.
Consequently, when the subject vehicle drives on a curved road and when an oncoming vehicle approaches on an oncoming lane toward the subject vehicle driving on the curved road, the conventional headlight system using the shade control unit incorporated into the subject vehicle may emit a glare type light to the oncoming vehicle because a long switching time. Especially, the conventional headlight system may have a high chance of an emission of the glare type light to the oncoming vehicle because a relative speed between the subject vehicle and the oncoming vehicle may become fast as compared with a forward vehicle moving forward in a forward direction of the subject vehicle.
In addition, a time while the conventional headlight system varies from the light distribution pattern to a high beam light distribution pattern to emit light on the above-described gone region of the oncoming vehicle after the oncoming vehicle passes through the subject vehicle may be also subject to a long time. Accordingly, a forward visibility of the subject vehicle may reduce during the time while the conventional headlight system varies from the light distribution pattern to the high beam light distribution pattern to emit light on the gone region of the oncoming vehicle.
Moreover, because the conventional headlight systems including the above-described ADB include at least one of the movable parts in a headlight, the headlight systems should become a complex structure. Therefore, the headlight systems may only be incorporated in limited vehicles, because the headlight used for the headlight systems may become big and also may decrease the possibility of car design.
The above-referenced Patent Documents and additional Patent Documents are listed below and are hereby incorporated with their English abstracts and specification in their entireties.    1. Patent Document No. 1: Japanese Patent Application Laid Open JP 2010-232081    2. Patent Document No. 2: Japanese Patent Application Laid Open JP 2012-151058    3. Patent Document No. 3: U.S. Pat. No. 8,373,182    4. Patent Document No. 4: U.S. Patent Publication No. 2013-0242100-A1    5. Patent Document No. 5: U.S. Pat. No. 8,251,560
The disclosed subject matter has been devised to consider the above and other problems, characteristics and features. Thus, exemplary embodiments of the disclosed subject matter can include headlight controllers which can provide a favorable light distribution pattern to safely drive at night in accordance with various traffic conditions, while preventing a right and left headlight from emitting a glare type light to oncoming vehicles and vehicles moving in a forward direction of a subject vehicle, even when the subject vehicle drives on a big curved road, and even when an oncoming vehicle approaches on an oncoming lane toward the subject vehicle and also passes through the subject vehicle.
In addition, exemplary embodiments of the disclosed subject matter can include vehicle headlight systems including an optical unit with a simple structure, which can be used as the right and left headlight for the above-described headlight controller. The optical unit does not include movable parts such as the conventional headlight, and therefore can expand possibilities for design so as to be able to harmonize with various vehicular designs.